The present invention relates in general to sewing machines and in particular to a new and useful device for producing sewing seam patterns of stitch groups for example button holes comprising a guide assembly for carrying a sewing machine which moves the sewing machine cyclically in a direction of stitch formation according to the motion of a displaceable clamping mechanism of the sewing machine.
In a device according to German Pat. No. 1,230,296, for producing a plurality of spaced buttonholes in a workpiece, such as a front part of a shirt, using a buttonhole sewing machine comprising a work clamping mechanism displaceable through a distance corresponding to the length of the buttonhole, a workpiece holder is provided by which, during the interval between two sewing operations, the workpiece is displaced through the interspace between two buttonholes. The workpiece or work holder is equipped with two clamps which are so spaced from each other that the work can be clamped in the area of the button tape, at its leading and trailing edges. The work clamps are mounted on the holder for pivoting toward and away from each other and they are operatively connected, through a linkage, to a part of the sewing machine stopping device, which is moved, before the start and after the termination of each individual sewing operation, in such a way that prior to the start of the sewing operation, the clamps are moved toward each other to slacken the work, so that the work may be freely moved relative to the stopped work holder in the area of the buttonhole to be sewn. Upon termination of a sewing operation, the clamps are moved away from each other to stretch the work to the proper extension between two buttonholes in the longitudinal direction of the button tape, for further displacement by the work holder.
Because of the slackening in the longitudinal direction, however, the work may very easily deform, due to its elasticity. With tricot, knitted fabrics and other highly elastic materials, this deformation is very extensive and not only causes puckering in the areas reinforced by sewing but also, since the folded edge of the work "springs up", a deviation of the fold edge from a straight line. With fancy, especially checkered materials, this is particularly conspicuous and therefore unacceptable. It is true that the so-called springing up of a folded button tape might be prevented to a large extent by ironing, however, further costs are incurred with such an additional operation, which should be avoided.